damp strawboard bathroom wall?

Question

We have a major problem in our bathroom, it turns out that the wall behind out tiles next to our bath is soaked. It appears that water has been leaking in through the grout and the consequences are horrible. 
After peeling back the tiles and mouldy adhesive, it turns out the wall is made of strawboard and is damp right through to the other side. 
We have been drying it out with a heater and have purchased some cement boards to fix to the wall once damp. Our plan is to PVA the wall then use 'Pink Grip' to put the cement boards up, followed by tiling the boards. The wall seemed to be drying out lovely until we noticed the other side of the wall (our bedroom) had damp lines appearing on the wall paper and the wallpaper was bubbling. It now looks like the wall is damp in our bedroom and also has black mould under the wall paper. 
We have been chatting and decided that we are going to put the heater on in our bedroom and the dehumidifier on in the bathroom to dry it out as much as possible, then PVA the bedroom wall, plasterboard it to cover the damp sections and then wallpaper, this coupled with the work in the bathroom we are hoping will sort this issue. 
We dont have the money to pull the wall down and rebuild so i would just like some advise to confirm we have the right ideas or to advise a different solution if anyone has any. 
Whatever we do it has to be done soon, we have a baby due next month and so this all needs to be sorted before she arrives. 

Thanks for taking the time to read this.

BB · Accepted Answer

Hi. Bill
You are panicking.
Straw board as any other board will hold moisture.
You have done everything right.
The damp that was in the bathroom is now moving out to the bedroom.
Be patient it will dry out and then you can redecorate.
You have solved the problem. 
BB.
Happy New Year and enjoy your baby.

Anonymous · Answer

You are doing the right thing.  If the structure of the wall is cavity then see if you can pump hot air into the cavity, say with a hair drier or hot air gun.  This will speed things up.  To stop the black mould from re-growing you will have to apply quite a lot of coats of bleach.  I have always used a paint brush for this to spread it all over the area and beyond.

Wendy · Answer

Once you`ve sorted out the damp problem and are ready to re-tile it is advisable to have the tiles silicone sealed before they are grouted to the wall. This involves submerging the whole tile into liquid silicone (for a few hours) which is absorbed throughout the entirety of the tile, the tiles are then dried over several days. You`ll need to go to a tile manufacturer that offers this service if you are unable to do this yourself (strict safety measures will be needed). Having the tiles sealed will help prevent wetness from your shower getting through to the wall.

Candid Chris · Answer

Sounds good but before you start covering things back up spray down everything remaining with some bleach-water to eliminate any black mold, than let dry real well.

Jeff · Answer

Since money is tight, I think your idea makes a lot of sense.  The only thing I would add is to get a spray bottle and put bleach water in it and spray down the moldy parts before you build, to try to slow down/stop the mold.

I'd recommend about 4 parts water to one part bleach, sprayed evenly.

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damp strawboard bathroom wall?

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